Pat McMahan owns the largest collection of agates in the United States and second largest in the world.

At his home in Cottonwood, McMahan has carefully identified, labeled and put over 7,000 specimens on display, some of which will be on display at the ninth annual Sedona Gem and Mineral Club Show and Sale on Saturday and Sunday, Oct. 17 and Oct. 18.

“It’s just an addiction I guess,” McMahan said. “These to me are a work of art.”

Agates in McMahan’s collection came from as far away as Russia, Africa and Turkey. Others he’s found in his home state of Arizona.

“Arizona is a wonderful place for collecting,” McMahan said. He estimates 70 percent of his collection was found in Arizona.

It’s taken McMahan 20 years to accumulate the collection he boasts today and most specimens he finds don’t make the cut. He said he only keeps 2 to 3 percent of the agates he finds and sells or trades the others. Those that do make it into his collection must have a complete pattern and no cracks.

And McMahan does the dirty work. He collects, identifies, cuts, cleans and polishes his own agates in a shop he built behind his home two years ago specifically for that purpose.

The shop is home to 17 antique rock saws, one of which was made in 1947.

“It’s a very consuming hobby,” McMahan said.

Aside from his work on his collection, McMahan was commissioned by Johann Zenz, from Austria, to work on a book that has become the world authority on agates, “Agates II.” The book was released approximately one month ago.

The book will be available at the show along with postcards featuring pieces from McMahan’s collection.

The show will be held at Sedona Red Rock High School at 995 Upper Red Rock Loop Road in West Sedona. Over 35 vendors will be in attendance and three speakers will be featured: Dr. Carleton Moore, authority on meteorites, Walt Wright, a specialist in petrified wood, and Susan Zepkin, specialist in metaphysical properties.

McMahan will give a slide show presentation on agates and Bob Yee will demonstrate sphere making.

The club meets at the Sedona Public Library from September through May on the third Tuesday of the month at 7 p.m. McMahan said guests are welcome to attend for free and sit in on the meetings.